Irregular Pop At Exhaust

I noticed a new problem on my drive today. F134, 67 CJ5. I noticed an irregular/random pop in the exhaust at idle. It is frequent, but irregular. Single pops. Too rich? Seemed to drive well with normal power.

 

What is your timing at?

 

Figured it out. Too rich. I leaned it out 1/4 turn and it stopped. Runs perfect again. While I’m here, what idle RPM do you all set? The FSM says 700, but I’m at about 760 and like it better there.

 

That works for you, run it. I think elevation plays a part so for someone up in a mountain state it could be different

 

Glenn, it just seems to run better with a little more rpm at idle. All subjective. No really data to support my “like” at that rpm. How about, it sounds better.

 

Can you still get it to hold back enough, on a steep downhill crawl?

 

Good point PeteL. Never thought that keeping the idle down would help with the “crawling” ability. I think I’ll knock it back to 700 and see how it works in 4 low on different obstacles.

 

You can always use the throttle cable on the dash to raise the idle when desired.

 

Idle mixture adjustment:
Warm engine
Rotate idle mix screw in (lean) till the engine RPM's drop
Counting rotations, rotate out till engine speed drops again
Half the turns back in (best idle)
or
Rotate screw out till the engine stops picking up RPM's, go 1/4 turn more (best lean idle)
I'm a fan of best lean idle.

Idle can be run where you like. These parameters are given to the masses for general driving and tune up adjustments. Once those are set, you can choose the best idle speed for your application.

One thing to think about with higher idle speeds is the wear on the mechanical advance in the distributor. Worn or missing springs, worn pivots and weights can kick the mechanical advance in much earlier. Not really an issue until you try timing and adjusting the engine. You can also uncover the vacuum advance port (for those applications).

 

Perhaps not entirely. If the throttle plate does not close to the designed degree, various circuits in the carb are affected. For instance causing backfiring when downshifting, reduced engine braking, or etc.

 

Absolutely.

However, usually, unless there other parts of the "tune up" that are seriously off, getting to the point where the plates are that far open means seriously high idle. Since most folks like an idle somewhere from 500 to 700RPM, I'm not sure if that applies.

Of course, we're talking about engines with minimal smog equipment. For those driving a 86 Cali CJ, being spot on can tend to be important.

 

Isn’t this an air mixture screw on the Solex? I thought that CCW made it leaner (i.e., adds more air).

 

The instructions are generic for about 90% of all carbs. If your carb has air bleeds, then you may have to modify them.